Magnetic-field dependence of chemical anomalies in CP stars

The dependence of the degree of anomaly of parameter Z of Geneva photometry (Z0 = Z _CP ?Z _norm.) on the average surface magnetic field Bs is analyzed. The Z0 value is proportional to the degree of anomaly of chemical composition. It was found that Bs → 0 corresponds Z0 → ?0.010÷ ?0.015, i.e., part of CP stars are virtually devoid of magnetic field, but exhibit chemical anomalies. This effect may be due to selection whereby only objects with strong chemical anomalies are classified as CP stars, thereby producing a deficit of stars with relatively weak anomalies. Moreover, CP stars have other sources of stabilization of their atmospheres besides the magnetic field, e.g., slow rotation. Formulas relating Z0 to Bs are derived.     

Synchronous <Emphasis Type="Italic">UBVR</Emphasis> photometry and spectroscopy of DI Cephei

We present our synchronous spectroscopy and photometry of DI Cep, a classical T Tauri star. The equivalent widths and radial velocities of the individual components and Hα, Hβ, D1 and D2 Na I, and HeI λ5876 Å emission line profiles exhibit variability. We have found a clear positive correlation between the brightness and equivalent width for the Hα and Hβ emission lines. The photometric and spectroscopic data are satisfactorily described in phases of a 9-day period. The expected magnetic field of the star has been estimated using existing magnetospheric models to be 655–1000 G. The star is suspected to be a binary.     

The investigation of nova-like variable MV Lyr during the 1999–2001 years

A peculiar nova-like MV Lyr was investigated. The CCD-observations of MV Lyr were continued in Crimea during the outbursts and quiescent states. Last year its behavior became non-typical for “anti-dwarf novae”. The length of its first deep minimum was 10 years. A modern state is characterized by very strong outbursts and very often changes of the stages. The periods 0. ^d 128 and 0. ^d 136 were obtained for 1998 and 1999 years accordingly. Possibly, a relation between the photometric period and the brightness exists.     

A moderate-resolution Nasmyth-focus spectrograph of the 6-m BTA telescope

We report on the development of a fast crossed-dispersion spectrograph (CRAB) mounted at the Nasmyth focus of the 6-m telescope. The spectrograph is designed for visible and near-infrared (3800–10 500 Å) CCD observations with the spectral resolution R=4000. We give the basic parameters of the optical scheme and the parameters of the echelle frame. We determined the gain involved in putting the spectrograph into observational practice and discuss the possible range of spectroscopic problems for which the instrument is optimal.     

Spectra Of Split Comet C/1999 S4 (Linear)

We obtained spectra of comet C/1999 S4 (LINEAR) with the UAGS spectrograph(long slit and CCD) installed on the 1-m Zeiss reflector of the SAO of the RAS(Northern Caucuses, Nizhny Arkhyz) on July 23/24, 26/27 and 27/28, 2000. OnJuly 22/23, before the splitting of the cometary nucleus, several emission lines,such as C₂, C₃, CN, NH, CH, NH₂, CO⁺, H₂O⁺ wereclearly identified in the spectra. The inspections of the CCD spectra obtainedon July 27/28, 2000 reveals only very weak emission lines superimposed on thesolar reflection spectrum. From analyzing the surface brightness profile of C₂ along the slit the velocity of separation of two secondary fragments (V = 10 km/h) and the energy of the fragment separation (E = 8.7 × 10¹⁵ erg) were estimated. A luminescence cometary continuum of 26% of the total continuum level is detected in the spectra of the comet at 5000 Å. Possible mechanisms of nucleus splitting are discussed.     

北京雷暴大风气候特征及短时临近预报方法

北京地区雷暴大风的预报准确率低而且时效短.为了提高对这种灾害性天气的预警能力,在气候统计的基础上,研究了潜势预报方法和临近预报算法.对1998-2007年134个雷暴大风过程的统计结果表明,北京地区绝大多数的雷暴大风具有下击暴流特征,而且冰雹的落区附近也是大风的爆发区之一.因此,负浮力的作用和对冰雹具有指示性意义的因子是研究雷暴大风预报方法应主要考虑的因素.500hPa环流背景分析表明,尽管绝大多数雷暴大风爆发时对流层中层有干空气侵入,但是还有少数个例产生在偏南暖湿气流中.目前,对后一类大风产生的机制仍然不清楚.研究表明,当对流层中层有干空气侵入时,有利于雷暴大风出现的环境条件是:下沉气流具有较大的不稳定性,同时对流层低层环境大气的温度直减率较大.此外,还讨论了经验指数--大风指数在北京地区的应用.基于上述的研究,形成了北京地区雷暴大风短时潜势预报方法,还使用相关分析和多元回归分析技术建立了基于雷达观测和环境条件的雷暴大风临近预报方程.个例分析表明,临近预报方程对于飑线和弓形回波等带来的地面大风具有一定的预报能力.     

Methods for the analysis of data from the Planetary Fourier Spectrometer on the Mars Express Mission

This work presents an algorithm for the scientific analysis of individual calibrated measurements from the Planetary Fourier spectrometer (PFS).The instrument, included in the scientific payload of the ESA Mars Express mission to Mars, acquires spectra in the range between 250 and 8200 cm⁻¹, with a sampling step of ∼1 cm⁻¹ and an effective resolution of ∼2 cm⁻¹. The observed radiance depends on several parameters of the atmosphere and surface of Mars as described by the radiative transfer equation. Adopting the very general formalism of Bayesian analysis, we determined which quantities are actually retrievable from individual measurements. Namely, they are: the surface temperature, the column density of dust and water ice aerosols in the atmosphere, the air temperature as a function of altitude (in the indicative range 5-45 km above the surface), the surface pressure, and the column density of water vapor and carbon monoxide. These evaluations are carried out taking into account the noise equivalent radiance (NER) of the instrument and the natural variabilities of the investigated parameters in the Martian environment, as estimated from the expectations of the European Martian Climate Dataset v3.1 (EMCD). Other parameters included in the radiative transfer equation shall be assumed as known, because they are not retrievable from individual measurements due to the instrumental NER or an underconstrained inverse problem: the surface emissivity in the thermal infrared, the optical properties of suspended dust and the analytical shape of dust concentration vs. altitude.During the development of the algorithm devoted to these studies, different approaches were evaluated on the basis of formal, computational and scientific considerations, with the aim to develop the general design of an integrated software package.The resulting code was extensively tested on a wide set of simulated PFS spectra. These spectra were computed from the atmospheric and surface conditions extracted from the EMCD, assumed to be representative of the Martian environment for different values of latitude, local time and season. Their comparison with the retrievals from simulated observations allowed us to evaluate the systematic and random errors affecting the procedures with respect to the different quantities involved. The code evaluates the surface temperature with an error in the order of 1 K, while the vertical air temperature profile is computed with an uncertainty less than 2 K from in the region between 5 and 20 km above the surface, increasing up to 7 K at 50 km. The column opacity of dust, measured in terms of integrated optical thickness at 1100 cm⁻¹, is computed with an error of around 0.13. The surface pressure determination is carried out with a typical uncertainty of 0.2-0.3 millibar. Several auxiliary tests allowed us to study the correlations between the different retrieval errors and the possible causes of incorrect PFS data interpretation. The choice of a suitable model for the dust optical properties is demonstrated to be particularly critical.This paper also presents the first discussion about application of the procedure to actual PFS Martian data. Despite the calibration issues still affecting the determination of absolute radiance in the near-infrared, the algorithm is able to achieve a satisfactory modeling of observations in a wide range of situations.     

The origin of the CN radical in comets: A review from observations and models

The origin of CN radicals in comets is not completely understood so far. We present a study of CN and HCN production rates and CN Haser scale lengths showing that: (1) at heliocentric distances larger than 3 AU, CN radicals could be entirely produced by HCN photolysis; (2) closer to the Sun, for a fraction of comets CN production rates are higher than HCN ones whereas (3) in the others, CN distribution cannot be explained by the HCN photolysis although CN and HCN production rates seem to be similar. Thus, when the comets are closer than 3 AU to the Sun, an additional process to the HCN photolysis seems to be required to explain the CN density in some comets.The photolysis of HC₃N or C₂N₂ could explain the CN origin. But the HC₃N production rate is probably too low to reproduce CN density profile, even if uncertainties on its photolysis leave the place for all possible conclusions. The presence of C₂N₂ in comets is a reliable hypothesis to explain the CN origin; thus, its detection is a challenging issue. Since C₂N₂ is very difficult to detect from ground-based observations, only in situ measurements or space observations could determine the contribution of this compound in the CN origin.Another hypothesis is a direct production of CN radicals by the photo- or thermal degradation of complex refractory organic compounds present on cometary grains. This process could explain the spatial profile of CN inside jets and the discrepancy noted in the isotopic ratio ¹⁴N/¹⁵N between CN and HCN. Laboratory studies of the thermal and UV-induced degradation of solid nitrogenated compounds are required to model and validate this hypothesis.     

The Dergaon (H5) chondrite: Fall,classification, petrological and chemical characteristics,cosmogenic effects,and noble gas records

Abstract— A multiple fall of a stony meteorite occurred near the town of Dergaon in Assam, India, on March 2, 2001. Several fragments weighing <2 kg and a single large fragment weighing ～10 kg were recovered from the strewn field, which extended over several tens of square kilometers. Chemical, petrographic, and oxygen isotopic studies indicate it to be, in most aspects, a typical H5 chondrite, except the unusually low K content of ～340 ppm. A cosmic ray exposure of 9.7 Ma is inferred from the cosmogenic noble gas records. Activities of eleven cosmogenic radionuclides were measured. ²⁶Al and ²²Na activities as well as the ²²Na/²⁶Al activity ratio are close to the values expected on the basis of solar modulation of galactic cosmic rays. The low ⁶⁰Co activity (<1 dpm/kg) is indicative of a small preatmospheric size of the meteorite. Cosmic ray heavy nuclei track densities in olivine grains range from ～106 cm^?2 in samples from the largest fragment to approximately (4–9) × 105 cm^?2 in one of the smaller fragments. The combined track, radionuclide, and noble gas data suggest a preatmospheric radius of ～20 cm for the Dergaon meteorite.     

蓝离散星研究现状(Ⅰ):形成机制

大量研究表明,蓝离散星的形成可能有多种机制,目前比较流行的形成机制可以概括为以下几类:密近双星系统的质量传输及双星并合、密集星场的恒星碰撞,以及包含双星系统的恒星间 (双星-单星、双星-双星)相互作用导致的恒星并合。与此同时,蓝离散星在各类恒星系统中的普遍存在,也使得研究这类恒星的形成及演化成为追踪恒星系统动力学演化、化学演化及积分光谱性质变化的有效指针。